On 22.12.2009 5:15, Walter Bright wrote:
Yigal Chripun wrote:
But that doesn't mean the idea itself isn't valid. Perhaps a different
language with different goals in mind can provide a much simpler non
convoluted implementation and semantics for the same idea?
You've shown in the past that you're willing to break backward
compatibility in the name of progress and experiment with new ideas.
You can make decisions that the C++ committee will never approve.
Doesn't that mean that this is at least worth a shot?
I believe that D's template constraint feature fills the bill, it does
everything Concepts purported to do, and more, in a simple and easily
explained manner, except check the template body against the constraint.
...and template overloading based on concept refinement. D requires
hacks to accomplish that:
template isFoo(T)
{
}
template isBar(T)
{
enum isBar = ... && isFoo!T;
}
template Foo(T) if (isFoo!T && !isBar!T /+ hack +/) {}
template Foo(T) if (isBar!T) {}
In the run-time domain, it would be analogous to requiring a parameter
to specify which interfaces the argument *should not* implement:
interface IFoo
{
}
interface IBar : IFoo
{
}
void foo (IBar a)
{
}
void foo ((IFoo && !IBar) a) // meh
{
}
Maybe it is not a significant shortcoming but it needs to be mentioned.
The latter is, in my not-so-humble opinion, a desirable feature but its
desirability is overwhelmed by the payment in complexity and
constrictions on the Concepts necessary to make it work.
